The cerebro-spinal system consists of the spinal cord and the brain. The brain in turn is made up of two principal subdivisions. First, there is the greater or upper brain, called the cerebrum; secondly, there is the lower or smaller brain, called the cerebellum. The cerebrum in turn consists of three parts: the convoluted _surface_ brain, the _middle_ brain and the _lower_ brain. So that in all we have the _surface_ brain, the _middle_ brain, the _lower_ brain and the _cerebellum_. All these parts consist of masses of brain cells with connecting nerve fibers. [Sidenote: Brains Parts and Functions] And now, as to the functions of these various parts. Beginning at the lowest one and moving upward, we find first that the _spinal cord_ consists of through lines of nerves running between the brain and the rest of the body. At the same time it contains within itself certain nerve centers that are sufficient for many simple bodily movements. These bodily movements are such as are instinctive or habitual and require no distinct act of the will for their performance. They are mere "reactions," without conscious, volitional impulse. Moving up one step higher, we find that the _cerebellum_ is the organ of equilibrium, and that it as well as the spinal cord operates independently of the conscious will, for no conscious effort of the will is required to make one reel from dizziness. As to the divisions of the greater brain or cerebrum, we want you to note that the _lower brain_ serves a double purpose. First, it is the channel through which pass through lines of communication to and from the upper brain and the mid-brain on the one hand and the rest of the body on the other. Secondly, it is itself a central office for the maintenance of certain vital functions, such as lung-breathing, heart-beating, saliva-secreting, swallowing, etc., all involuntary and unconscious in the sense that consciousness is not necessary to their performance. The next higher division, or _mid-brain_, is a large region from which the conscious will issues its edicts regulating all voluntary bodily movements. It is also the seat of certain special senses, such as sight. Lastly, the _surface brain_, known as the cortex, is the interpretative and reflective center, the abode of memory, intellect and will. [Sidenote: Drunkenness and Brain Efficiency]